1. Field of the Invention
The invention refers to a device for intermittently subjecting axially shiftable bits of a cutting head to the action of pressurized fluid, in which device the bits are pressed in outward direction by a percussion piston under the action of the pressurized fluid and the percussion piston is retracted by the force of reaction of the bits with supply of pressurized fluid being deactivated.
2. Description of the Prior Art
Cutting heads of this type are used in partial cut cutting machines in which at least one cutting head is rotatably supported on a universally swivellable cutting arm. In most cases, two cutting heads are rotatably supported on such cutting arms for rotating around an axis crossing or intersecting the axis of the cutting arm. It is known to support the bits of such a cutting head for effecting a limited axial shifting stroke within bit holders, noting that the shifting movement of the bit has, for example, been used for opening a valve for the purpose of spraying water via nozzles onto the mine face.
From U.S. Pat. No. 4,555,143, the disclosure of which is incorporated herein by reference, there has already become known a process and a device for introducing water via distributing bolts into passages of a cutting head. In this known arrangement, the bit holder has a percussion piston arranged behind the bit and exerting, for the purpose of improving the efficiency of cutting work, a percussion action on the bit by being intermittently subjected to the action of pressurized fluid. The distributor provided in this known construction was arranged in proximity of the axis and stationary relative to the rotating cutting head. On account of the small dimension in radial direction of the distributor having substantially the shape of a bolt, only a low number of perforations could be provided along the circumference of the distributor, which resulted in only low impact frequencies. Cutting heads of the usually mentioned type are usually operated with relatively low rotating speed in the order of 60 rpm, so that the impact frequency observed was also limited on account of this fact.